TTC with best friends husband

Hello it's been a while. I've read many books on how to be the perfect side woman (mistress) and I am now TTC with Leopardo who is married currently. He wants twins with me and we've tried the Twinning Position but no luck yet. I've gotten pregnant with a singleton but quickly aborted when we discovered it wasn't twins.

Leopardo is only 4 inches so maybe that's it? Any ideas and suggestions on how to TTC twins? Anything will help. Namaste!